The present invention relates to a device or portable administering apparatus for administering a fluid product, in particular medical substances or a drug in liquid form. In particular the invention relates to a portable infusion pump and/or infusion systems such as insulin pumps. Such a device is referred to in the following as an administering device.
In the case of various diseases, it can be necessary to administer a patient over a longer period of time with a drug which is provided in liquid form, for example an insulin preparation or a haemodiluting drug such as heparin. Compact portable infusion apparatuses are known for this purpose and are continuously carried around close to the body by the patient. In most cases, a carpule is provided as the drug container in such infusion apparatus, i.e. a plastic or glass container comprising a plug which can be moved within it. The carpule (often also referred to as a carpoule, an ampoule or a reservoir) is connected to an infusion set, the cannula of which feeds into the body tissue of the patient. The plug or stopper is advanced in the carpule by a suitable drive, for example, a spring drive or an electric motor, and the drug is thus expelled from the carpule. As soon as the carpule is empty, it is removed from the infusion apparatus and replaced with a new carpule.
In many portable infusion apparatuses, the plug is advanced in the carpule via a threaded rod which acts as a piston rod for the plug. A nut which is mounted such that it is rotatable but fixed against shifting runs on the threaded rod and is driven by an electric motor. Rotating the nut advances the threaded rod, wherein the electric motor is, in general, arranged next to the carpule in order to limit the length of the infusion apparatus and to simplify exchanging the carpule.
U.S. Pat. No. 6,248,093 B1 discloses an infusion apparatus in which the drive motor and a gear system are arranged coaxially with the drug reservoir. The plug of the drug reservoir is advanced by a sleeve-like advancing element which is connected via an inner thread to a drive screw, which is driven by the motor, and thus linearly advanced. In its initial position, the advancing element at least partially surrounds the gear system of the motor, wherein the advancing element is a part of the base unit, while the plug is part of the exchangeable drug reservoir. The advancing element and the plug are therefore embodied such that they can be separated from each other. In order to ensure that the drug is not undesirably expelled by fluctuations in the ambient pressure, the advancing element and the plug are connected such that the connection can also absorb tensile forces while the infusion apparatus is in operation. In this way, the plug necessarily follows the movement of the advancing element and cannot be advanced, by pressure fluctuations, further than is predetermined by the position of the advancing element. When the drug reservoir is exchanged, the plug and the advancing element are separated from each other by a rotational movement. The advancing element is then moved back into its initial position by the motor. On the one hand, this arrangement requires a relatively complicated connection between the plug and the advancing element; particular steps also have to be taken in case a drug reservoir which is not completely filled is used.
An infusion apparatus is known from EP 0 985 419 A1 in which the drive motor and a drug reservoir are arranged antiparallel with respect to each other, wherein a gear system transmits the drive movement from the motor to an advancing element which is arranged coaxially with respect to the reservoir and in turn moves the plug provided in the drug reservoir, thus displacing the drug from the reservoir. A so-called infusion set adaptor is attached to the exit of the drug reservoir and channels the drug into an infusion set. In order to ensure that the drug is not undesirably expelled by fluctuations in the ambient pressure, a threshold value valve is arranged in the infusion set adaptor and requires a particular drive pressure in order to enable liquid to be transported through the infusion set adaptor at all. As compared to the variant described above, in which the plug is retained by the advancing element, the threshold value valve has the advantage that standard carpules for the infusion apparatus can be used; in particular, specially shaped plugs are not required. It is, however, known that when the threshold value valve is a membrane valve, an inaccurate positioning of the valve membrane can potentially lead to malfunctions and in particular valve leakage, and that accurately positioning the membrane presents a production-related challenge.
U.S. Pat. No. 5,993,423 describes a portable automatic syringe device and an injection needle unit thereof.
U.S. Pat. No. 7,597,682 B2 describes an external infusion device for infusion of a fluid into a body from a reservoir including a drive system, a housing, an electronic control circuitry and at least one vent port. The vent port in the housing permits the passage of air into and out of the housing and inhibits the passage of liquids into the housing.
A user of an administering device may travel through various elevations, which might occur when hiking in the mountains or travelling in an airplane, so that differential pressures can arise between the interior of the air tight or water-resistant pump housing and the outside or atmosphere. Once the pressure in the housing exceeds the external atmospheric pressure, resulting forces could cause the reservoir plug or reservoir piston to be driven inwards, thus delivering unwanted medication. Problems with the correct functioning of the administering device may also occur in case the outside atmospheric pressure exceeds the inside pressure of the housing.
It is desirable to have an administering device which guarantees safe operation among various atmospheric pressures.